Buddho

"Buddho" is used by many Thais, especially those who have been taught in the Forest Tradition. It is used to to build concentration, and that is all. What we do is to say "Bud" when we breath in, and "dho" when we breath out. It is not a necessity even. We can use "Dhamma/Dhammo", "Sangha", or other words of our own choosing. The main point is that this is a tool for building concentration.

When we repeatedly say "Buddho", "Buddho", the word will eventually disappear, and then concentration will only be on the breath. When the breath becomes shallower, and shallower, and there is no longer any breath to follow, just stay with the knowing or one-pointed knowing. Ignore all kinds of experiences (as in lights, colours, body sensations, visions, etc).

That is all. A tool to gain samadhi, concentration.There is no visualization involved.

In fact, visualization is discouraged as it can lead us to "follow" any mind-made stories that may be the result of that visualization.Usually, "Buddho"/other tools are used to gain enough samadhi to do vipassana. And both can be done again and again in circle (as samadhi reinforces vipassana, and vipassana reinforces samadhi).

And if possible, this should follow by mindfullness throughout the day, in all body positions. But this should be done in a relaxed way, be natural without force.